<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
		
		<!-- 
			string  boolean   -> number

		 -->
		 
		 <script type="text/javascript">
		 	
			var str = "10"   
			str =  false  // true  1  false 0
			console.log(typeof str);
			console.log("str="+str);
			
			console.log("------------Number(str)--------------");
			str =   Number(str)   //  a1  ->  NaN     not a number   NaN  -> number
			console.log(typeof str);
			console.log("str="+str);
		
			// console.log("------------parseInt(str)--------------");
			// str =  parseInt(str)   //  boolean  ->  NaN
			// console.log(typeof str);
			// console.log("str="+str);
			
			// console.log("------------数学运算--------------");
			
			// str = str / 1
			// console.log(typeof str);
			// console.log("str="+str);
			
			
			
			
			
			
		
			
		 </script>
	</body>
</html>
